Molecular Cytogenetics enables the analysis of chromosomal changes over a broad range of focus, from whole genome composition or organization to specific gene copy number or location. It provides a comprehensive genomic context for global or targeted cell biology studies. In contrast to most other approaches, it enables a cell-by-cell survey of chromosomal content, revealing heterogeneity and possible associations within that heterogeneity. Thus cytogenetic analysis remains a simple and efficient first step towards identifying novel areas of genomic change. The Molecular Cytogenetics Core provides MSKCC investigators with effective chromosome-based analyses for human or research animal cells. It processes samples from primary cells, cell lines, or archival tissue, performs chromosome analysis on research samples, using conventional Cytogenetics (chromosome banding and karyotyping) and molecular Cytogenetics procedures based on fluorescence in situ hybridization (FISH), including Spectral Karyotyping (SKY). The Core staff works with investigators to design the most appropriate and efficient analysis for their needs and produces customized probes for specific projects. The Core has assembled a broad range of molecular Cytogenetics resources for human and mouse analysis, including plasmid and BAG clone stocks, as well as chromosome paints. Chromosome analysis is an integral part of research focusing on genomic instability. The Core's experience in karyotyping and chromosome identification provides valuable support to investigators attempting to understand the basis of chromosomal instability in cancer. In addition to specific research applications, the Core also provides an essential function in maintaining Good Laboratory Practice for MSKCC research projects that use cultured cell lines. Karyotype analysis provides basic confirmation and documentation of cell line identity, and is used to monitor chromosomal integrity.